The overall aim of this work is to investigate effects of current and predicted levels of long and middle range (UV-A, 320-400nm and UV-B, 280- 320 nm) ultraviolet radiation on photosynthetic systems, particularly phytoplankton and reef building corals. MBRS students have in the past and will continue to actively participate in several aspects of this work. The specific objectives of the MBRS student's research consist of training not only in proper use of the equipment, but more importantly in the ways of asking scientific questions and developing research projects to answer the questions so formulated. Specific research goals are 1) To elucidate effects of chronic exposure to UV-B on single celled algae, 2) To determine if there are species specific difference in tolerance to UV that might result in shifts in community composition under UV stress. The exposure experiments use two UV sources: 1) natural solar radiation filtered, when experimental protocol requires, through selective filters and 2) artificial radiation produced by our Xenon arc "solar simulator". The MBRS students receive training in quantification of light and UV radiation and in designing and building incubation systems. The effects of exposure are monitored through analysis of growth rates and composition of both photosynthetic and UV-absorbing pigments. Additionally photosynthetic capacity is measured before and after exposure to UV using 14C fixation. Effects of UV stress on species composition are initially being followed through two-species competition experiments run under differing levels of UV radiation.